In October 1968, Allen Latham, Jr. presented a paper entitled "A New Approach to Automated Centrifugal Processing of Blood" at the 21st Annual Meeting of the American Association of Blood Banks, in which he described a system for processing blood using an expendable, or disposable, centrifuge rotor in the form of a relatively inexpensive bowl. The system was proposed for use in a number of pheresis procedures, such as plasmapheresis, plateletpheresis and thrombocytapheresis. In these processes, whole blood is taken from a donor and various blood components are separated from the whole blood and harvested while some components are returned to the donor. The system was also suggested for use in cell washing, such as in deglycerolization, in which thawed deglycerized red cells are washed to remove the glycerene preservative before being infused in a patient.
In operation, the bowl is held in a chuck which is attached to a spindle and driven by a motor. The bowl consists of a rotor, or bowl body portion in which blood component is separated and a stator portion consisting of an input and output port. A rotary seal couples the stator to the rotor. One side of the input port is connected through a first peristaltic pump to a source of whole blood from a donor and the other side is in fluid communication with a fractionation volume in the rotor. Anticoagulant is mixed with the whole blood prior to entry into the centrifuge bowl.
The rotor is rotated at a fixed speed and various blood fractions are collected at the output port and directed into appropriate containers, such as plastic bags, by diverting the flow through plastic tubing in accordance with the setting of three-way clamp/switches.
Fractionation within the centrifuge is determined by the relative densities of the different cell components being separated and collected. The various cell fractions pass through the outlet port of the centrifuge bowl by progressive displacement from the lower portion of the bowl.
The bowl consists of two major subassemblies. One is a rotatable bowl body with an inner cylindrical core mounted coaxial to a central longitudinal axis through the bowl body. The other is a rotary seal and header assembly, which is provided on top of the bowl body.
The header assembly must remain fixed, since the inlet and outlet tubing to, or from, a donor or patient, is coupled to it. The rotary seal provides the appropriate interface between the fixed header and the rotating bowl body.
The system, including the bowl, interconnecting tubing and receptacles, are connected together and sterilized in advance of use, so that they arrive in sterile form ready for immediate use. All parts, other than the rotary seal assembly, are generally made from blood-compatible plastic, such as polycarbonate (for the bowl), or polyethylene (for the tubing and receptacles).
While the design of such blood processing centrifuge bowls, now called the Latham bowl, has evolved over the years, the basic structure remains the same and one of the key elements is still the rotary seal.
The rotary seal must be capable of meeting a number of stringent and, in some cases, opposing requirements.
1. Sterile air is present in the bowl when shipped. The seal must be capable of minimizing air leakage out of the bowl or introduction of non-sterile air into the bowl under prescribed ambient pressure ranges.
2. Blood components come in contact with portions of the seal. The seal must therefore minimize frictional heating and be capable of rapidly dissipating any heat generated to avoid thermal damage to the blood components. Also, the materials used in the seal which come in contact with the blood should preferably be blood-compatible and non-toxic.
3. The generation of particulates from the seal should be minimized and any particulates so generated should be prevented from entering the bowl body.
4. Since the bowl is part of a disposable assembly, it should be made of simple, low-cost, reproducible parts, easily assembled and tested and reliable in order to produce an economically reproducible and reliable system.
One of the earlier Latham bowl seals is disclosed in U.S. Pat. No. 3,409,213 and comprises a dynamic seal and a secondary seal. The dynamic seal is formed of an upper rotating ring member of carbon or graphite, which rotates against a non-rotating shoulder of an aluminum inlet tube. The shoulder is coated with oxide to provide a low friction bearing surface. The secondary seal is a static seal comprised of an elastomer member formed of silicone rubber.
A more complicated rotary-seal system was developed by Bellco of Mirandola, Italy, and is described in U.S. Pat. No. 4,300,717 in connection with FIG. 1 thereof. Briefly, this seal consisted of a dynamic seal comprising an upper non-rotatable graphite ring member which rested on top of a lower rotatable ceramic ring attached to first and second adapter rings formed respectively of aluminum and plastic. The adapter rings, in turn, are affixed to the bowl body by bonding the second adapter ring to the bowl neck at the periphery thereof. A secondary seal is formed by an elastomeric diaphragm attached to a third adapter ring which, in turn, is affixed to the upper graphite ring member.
In U.S. Pat. No. 4,300,717, Latham describes, in connection with FIG. 6, an improved rotary seal which also uses a non-rotatable graphite upper ring, as in the Bellco bowl, and a lower rotatable ceramic ring, which is directly affixed to the bowl body at the neck thereof. This seal incorporated an area of non-contact radially inwardly from the area of contact for entrapping particles generated in the area of contact, so that such particles are ingested in the area of contact and eventually expelled, so that they do not enter the bowl body section and co-mingle with blood components.
In an alternate embodiment (FIG. 8) of the '717 patent, an intermediate metal adapter ring is interposed between the ceramic lower ring and the neck of the bowl body to help dissipate heat.